Image capturing apparatus having distance measurement function

ABSTRACT

An image capturing apparatus illuminates an object and captures an image of the object using the reflected light from the object. The image capturing apparatus includes an image sensor for capturing an image of the object by receiving reflected light, distance-measuring light-emitting devices for irradiating the object with spot light, and a control circuit for driving the distance-measuring light-emitting devices, detecting the spot light positions of the distance-measuring light-emitting devices from an image captured by the image sensor, and obtaining the distance to the object. The image sensor provided for capturing an image of the object can be used as a photodetector device for distance measurement. With this, it becomes unnecessary to separately provide a photodetector device for distance measurement, which enables miniaturization of the image capturing apparatus, as well as cost reduction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2006-057494, filed on Mar. 3,2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image capturing apparatus having adistance measurement function for measuring a distance of an object andcapturing an image of the object, and more particularly an imagecapturing apparatus for measuring a distance to the object so as todetect whether the object exists in an image capturing range.

2. Description of the Related Art

An image capturing apparatus for capturing an image in a predeterminedrange of an object by irradiating the object with uniform light iswidely used. In an image processing system using an image captured bysuch the image capturing apparatus, a sharp image is particularlyrequired.

For example, with the development of biometric technologies in recentyears, there have been provided a variety of apparatuses for personalidentification by which an individual can be distinguished by capturingan image of a living body by which an individual can be distinguishedand recognizing a feature of the living body, for example, fingerprintsof limbs, eye retinas, face and blood vessels.

In particular, blood vessels and skin patterns of a palm and a fingerare suitable for reliable personal authentication, because a relativelylarge amount of personal feature data may be obtained therefrom.Further, it is believed that the patterns of blood vessels (veins) donot change from the time of an embryo throughout the lifetime of anyperson, and that no identical pattern exists among any persons withoutexception, which are therefore suitable for personal authentication.FIGS. 19 through 22 show explanation diagrams of the conventional bloodvessel image authentication technique. As shown in FIG. 19, at the timeof registration or authentication, a user puts a palm of a hand 110close to an image capturing apparatus 100. The image capturing apparatus100 emits an ear infrared ray, and irradiates it the palm of the hand110. The image capturing apparatus 100 receives the near infrared rayreflected from the palm of hand 110 by a sensor.

As shown in FIG. 20, hemoglobin in the red corpuscle flowing in a veinloses oxygen. Such the hemoglobin (deoxidized hemoglobin) absorbs thenear infrared of the vicinity of 760 nm in wavelength. Accordingly, whenthe palm is irradiated with the near infrared, reflection is reduced ina portion in which a vein exists. Thus, by the degree of strength of thereflected near infrared, the location of veins can be recognized.

As shown in FIG. 19, first, the user registers a vein image data of theown palm into a server or a card, using the image capturing apparatus100 shown in FIG. 19. Next, to perform personal authentication, the usermakes the vein image data of the own palm to be read, using the imagecapturing apparatus 100 shown in FIG. 19.

The personal authentication is performed by collating the registeredvein image, which is extracted using a user ID, with a vein pattern inthe collation vein image being read above. For example, in the case ofthe collation of the vein patterns between the registered image and thecollation image as shown in FIG. 21, the person is authenticated asgenuine. Meanwhile, in the case of the collation of the vein patternsbetween the registered image and the collation image as shown in FIG.22, the person is not authenticated as genuine (see Japanese UnexaminedPatent Publication No. 2004-062826, FIGS. 2-9).

For such the biometric authentication or the like, it is necessary tocapture an image of an object (a portion of a human body in case of thebiometric authentication) in a non-contact manner. For this purpose, theimage capturing apparatus 100 emits light producing uniform lightintensity in a certain image capturing range (distance and area),receives the reflected light of the above image capturing range by asensor, and outputs a captured image signal as an electric signal.

FIGS. 23 and 24 show explanation diagrams of the conventional imagecapturing apparatus. As shown in FIGS. 23 and 24, the image capturingapparatus 100 includes an image capturing unit 120 at the center, and inthe periphery thereof, a plurality of light-emitting devices 130-1 to130-8. The dotted lines shown in FIG. 23 represent the range of thelight having uniform intensity emitted from an individual light-emittingdevice among the plurality of light-emitting devices 130-1 to 130-8.

As such, by disposing a plurality of (here, eight) point light sourcesin the periphery of image capturing unit 120, the image capturing rangeof the image capturing unit 120 can be irradiated with the light ofuniform intensity. Meanwhile, image capturing unit 120 includes aphotoelectric conversion unit 122 such as a CMOS sensor, and an opticalsystem 124 such as a lens. Since the photoelectric conversion device122, which is a plane photodetector device, has a predetermined lightreceiving area, a predetermined optical distance is required to guidethe reflected light of the image capturing range onto thelight-receiving plane of the photoelectric conversion device 122. Forthis purpose, a lens 124 such as a fish eye lens is disposed between thephotoelectric conversion unit 122 and the object, so that an image ofthe predetermined image capturing range is projected onto thelight-receiving plane of photoelectric conversion device 122.

Thus, conventionally, in order to irradiate the object with each pointlight source element 130-1 to 130-8 by sharing a predetermined imagecapturing range, the point light source elements 130-1 to 130-8 havebeen disposed apart from each other, as shown in FIG. 23. Also, in orderto supply the light of predetermined uniform intensity to the imagecapturing range, the point light source elements 130-1 to 130-8 havebeen disposed nearer to the object than the photoelectric conversiondevice 122, as shown in FIG. 24 (see WO 2004/088588, FIGS. 1 and 6).

Further, in such the image capturing apparatus, it is necessary todetect whether the object is positioned at a focal distance.Conventionally, an optical distance sensor having a light emissionportion and a light reception portion has been provided in the imagecapturing apparatus, so as to measure the distance to the object (see WO2004/088979, FIGS. 1 and 5). For example, the optical distance sensorhas been provided between the point light source 130-4 and the imagecapturing unit 120 shown in FIG. 24.

In the above conventional image capturing apparatus, the distance sensorincludes the light emission portion and the light reception portion.Since the distance is measured from the position of the reflected light,it has been necessary to dispose the light reception portion apart fromthe light emission portion. This causes the sensor of interest to becomea large size. Also, miniaturization of the image capturing apparatus hasbeen difficult and there has been a restriction when incorporating theimage capturing apparatus into equipment.

Also, in order to detect the inclination of the object also, it isnecessary to mount a plurality of distance sensors, which further causesdifficulty in miniaturizing the image capturing apparatus withrestriction to incorporate into equipment, and impediment to costreduction.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animage capturing apparatus having a distance measurement function, with aminiaturized configuration even when the distance measurement functionis added.

It is another object of the present invention to provide an imagecapturing apparatus having a distance measurement function, enablingcost reduction even when the distance measurement function is added.

It is still another object of the present invention to provide an imagecapturing apparatus having a distance measurement function, enablingeasy detection of the distance to the object with miniaturization.

In order to achieve the aforementioned objects, according to the presentinvention, an image capturing apparatus for capturing an image of anobject by illuminating the object and receiving reflected light from theobject, and includes: an image sensor for capturing the image byreceiving the reflected light; distance-measuring light-emitting devicesfor irradiating the object with spot light; and a control circuit fordriving the distance-measuring light-emitting devices, detecting thespot light positions of the distance-measuring light-emitting devicesfrom the image captured by the image sensor, and obtaining a distance tothe object from the detected spot light positions at the time of thedistance measurement.

Further, according to the present invention, preferably, thedistance-measuring light-emitting devices are disposed to the imagesensor in the positions of irradiating within an image capturing rangeof the image sensor with the spot light.

Still further, according to the present invention, preferably, thedistance-measuring light-emitting devices are constituted of at leastthree distance-measuring light-emitting devices disposed in differentpositions centered at the image sensor.

Further, according to the present invention, preferably, the above atleast three distance-measuring light-emitting devices are disposed inopposite positions centered at the image sensor.

Further, according to the present invention, preferably, the controlcircuit detects the spot light position of each distance-measuringlight-emitting device from the image captured by the image sensor, andobtains an inclination of the object from the detected positions.

Further, according to the present invention, preferably, thedistance-measuring light-emitting devices are mounted on a circuit boardhaving the image sensor mounted thereon.

Further, according to the present invention, preferably, an illuminationmechanism for illuminating the object at the time of image capturing isdisposed in the periphery of the image sensor, and thedistance-measuring light-emitting devices are disposed on the outersides of the illumination mechanism.

Further, according to the present invention, preferably, theillumination mechanism includes: a plurality of light-emitting devicesmounted in the peripheral positions of the image sensor; a ring-shapedlight guide member for guiding the light of the plurality oflight-emitting devices to an image capturing range, and illuminating theimage capturing range; and further includes an optical unit accommodatedinside the ring of the ring-shaped light guide member and for guidingthe reflected light of the object in the illuminated image capturingrange to the image sensor.

Further, according to the present invention, preferably, the imagecapturing apparatus further includes a circuit board having the imagesensor, the distance-measuring light-emitting devices, and the pluralityof light-emitting devices being mounted thereon.

Further, according to the present invention, preferably, the pluralityof light-emitting devices are mounted on the circuit board atpredetermined intervals along a circle in the periphery of the imagesensor, and the light guide member has a ring-shaped structurecorresponding to the circle.

Further, according to the present invention, preferably, a diffusionplate for diffusing the light of the light-emitting devices is disposedbetween the ring-shaped light guide member and the plurality oflight-emitting devices.

Further, according to the present invention, preferably, the pluralityof light-emitting devices are configured of light-emitting devicesemitting infrared rays, and at least on the incident plane of theoptical unit, an optical filter for filtering the visible light isdisposed.

Further, according to the present invention, preferably, the light guidemember includes: a lower end portion for guiding the light of thelight-emitting devices; an upper end portion for outputting the light inthe image capturing range; and a light guide portion for guiding thelight of the light-emitting devices from the lower end portion to theupper end portion.

Further, according to the present invention, preferably, the imagesensor images a portion of a living body.

According to the present invention, the image capturing apparatusincludes an image sensor for capturing an image of an object byreceiving reflected light, distance-measuring light-emitting devices forirradiating the object with spot light, and, at the time of distancemeasurement, a control circuit for driving the distance-measuringlight-emitting devices and detecting the spot light positions of thedistance-measuring light-emitting devices from an image captured by theimage sensor, thereby obtaining the distance to the object. Accordingly,the image sensor provided for capturing an image of the object can beused as a photodetector device for distance measurement. With this, itbecomes unnecessary to separately provide a photodetector device fordistance measurement, which enables miniaturization of the imagecapturing apparatus, as well as cost reduction.

Further scopes and features of the present invention will become moreapparent by the following description of the embodiments with theaccompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of an image capturing apparatusaccording to one embodiment of the present invention.

FIG. 2 shows an exploded structural view of the image capturingapparatus shown in FIG. 1.

FIG. 3 shows a component layout diagram of the circuit board shown inFIG. 2.

FIG. 4 shows an explanation diagram of the relationship between alight-emitting device and a photodetector device shown in FIG. 2.

FIG. 5 shows an assembly diagram of the decomposed components shown inFIG. 2.

FIG. 6 shows a configuration diagram of the external finishingcomponents shown in FIG. 1.

FIG. 7 shows a configuration diagram of the assembly of the assembledbody shown in FIG. 2.

FIG. 8 shows an outer view of the image capturing apparatus shown inFIG. 1.

FIG. 9 shows an explanation diagram of the illumination system shown inFIG. 1.

FIG. 10 shows a configuration diagram of the light guide member and thelight-emitting device shown in FIG. 9.

FIG. 11 shows a relation diagram of the emission intensity distributionof the light-emitting device, and the lower end portion of the lightguide member shown in FIG. 10.

FIG. 12 shows a first operation explanation diagram of the light guidemember shown in FIG. 10.

FIG. 13 shows a second operation explanation diagram of the light guidemember shown in FIG. 10.

FIG. 14 shows a third operation explanation diagram of the light guidemember shown in FIG. 10.

FIG. 15 shows a light intensity distribution diagram using the lightguide member shown in FIG. 10.

FIG. 16 shows a block diagram of a control circuit for the imagecapturing apparatus shown in FIG. 1.

FIG. 17 shows an imaging process flowchart of the control circuit shownin FIG. 16.

FIG. 18 shows an explanation diagram of distance measurement operationusing the configuration shown in FIG. 16.

FIG. 19 shows an explanation diagram of the conventional palm imagecapturing apparatus.

FIG. 20 shows a principle explanation diagram of the conventional palmimage capturing apparatus.

FIG. 21 shows an explanation diagram of the conventional palmauthentication technique.

FIG. 22 shows another explanation diagram of the conventional palmauthentication technique.

FIG. 23 shows an explanation diagram of an illumination configuration inthe conventional image capturing apparatus.

FIG. 24 shows a configuration diagram of the conventional imagecapturing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the present invention is describedhereinafter referring to the charts and drawings, in the order of animage capturing apparatus configuration, an illumination mechanism, animage processing configuration, and other embodiments. However, it is tobe noted that the scope of the present invention is not limited to theembodiments described below.

Image Capturing Apparatus

FIG. 1 shows a cross-sectional view of an image capturing apparatusaccording to one embodiment of the present invention; FIG. 2 shows anexploded structural view of the image capturing apparatus shown in FIG.1; FIG. 3 shows a top plan view of the circuit board shown in FIGS. 1and 2; FIG. 4 shows an operation explanation diagram of a light-emittingdevice and a photodetector device shown in FIG. 3; FIG. 5 shows anassembly diagram when the structures shown in FIG. 2 are assembled; FIG.6 shows a configuration diagram of the external case shown in FIG. 1;FIG. 7 shows a configuration diagram when the assembled body shown inFIG. 2 is housed in the external case; and FIG. 8 shows an outer view ofthe image capturing apparatus shown in FIG. 1.

Prior to the description of the configuration shown in FIG. 1, referringto FIGS. 2 through 7, the configuration of each portion illustrated inFIG. 1 is described. As shown in FIG. 2, an image sensor 30 such as aCMOS image sensor and a polarizing plate 32 are disposed at the centerof a camera substrate 20. In the periphery of the image sensor 30 of thecamera substrate 20, a plurality of light-emitting devices 22, 24 andphotodetector devices 26 are mounted.

Describing in more detail with reference to FIG. 3, the image sensor 30is mounted at the center of the camera substrate 20, and the polarizingplate 32 is pasted upon the image sensor 30. Along the circle in theperiphery of the image sensor 30 of the camera substrate 20, a pluralityof light-emitting devices 22, 24 and photodetector devices 26 aremounted.

Between each the above first light-emitting device 22 and each thesecond light-emitting device 24, the photo-detector device (photodiode)26 is disposed. As shown in FIG. 4, the above photodetector device 26 isprovided for receiving the light from both the first light-emittingdevice 22 and the light from the second light-emitting device 24(reflected light from a diffusion plate 44 described later), therebyperforming APC (automatic power control) of the first light-emittingdevice 22 and the second light-emitting device 24.

The above first light-emitting device 22 and the second light-emittingdevice 24 are driven for emission at individual timing. In the aboveexample, in order to independently perform automatic power control ofeach the first and second light-emitting device 22, 24, which emitslight at individual timing, one photodetector device 26 is disposedbetween the first light-emitting device 22 and the second light-emittingdevice 24 so as to receive the light from the first and secondlight-emitting devices 22, 24. Thus, the number of photodetector devicesfor APC control can be reduced.

Further, at the four corners of the camera substrate 20, fourdistance-measuring light-emitting devices 52 are provided for measuringthe distance to the object. As shown in FIG. 3, the above fourdistance-measuring light-emitting devices 52 are disposed on thediagonal lines of the camera substrate 20, at the farthest positions onthe diagonal lines so that each distance therebetween becomes farthest.From the distances measured by the above four distance-measuringlight-emitting devices 52, the inclination of the object (here, palm) isdetected.

In brief, on a single camera substrate 20, there are providedillumination systems 22, 24, 26 and imaging systems 30, 32 for imagingthe object, as well as a distance-measuring system 52.

Now, referring back to FIG. 2, in the upper direction of thelight-emitting devices 22, 24 of the camera substrate 20, there areprovided four diffusion plates 44 and four polarizing plates 42. Theabove diffusion plates 44 and the polarizing plates 42 are pasted ontothe polarization/diffusion plate holders 46 being attached on the foursides of the camera substrate 20. Each diffusion plate 44 diffuses, to acertain extent, the emission distribution of the directive light emittedfrom the first and second light-emitting devices 22, 24. Each polarizingplate 42 converts natural light emitted from the first and secondlight-emitting devices 22, 24 to linearly polarized light.

In the upper direction of the four polarizing plates 42, a ring-shapedlight guide member 10 is provided. The light guide member 10 is formedof, for example, resin, and guides the light from the first and secondlight-emitting devices 22, 24 of the camera substrate 20 in the upwarddirection, so as to irradiate the object with uniform light. To fit thedispositions of the light-emitting devices 22, 24 of the camerasubstrate 20, the light guide member 10 has a ring-shaped structure. Aswill be described in FIG. 9 and after, the light guide member 10 guidesthe light emitted from the first and second light-emitting devices 22,24 to the upward direction, so that the object is irradiated withuniform light.

Further, an optical unit 34 is attached to the camera substrate 20 onthe image sensor 30 disposed in the approximate center of the camerasubstrate 20, and inside the ring-shaped light guide member 10. Theoptical unit 34 is constituted of a lens optical system such as aconverging lens.

An aperture 50 is mounted on the distance-measuring light-emittingdevice 52 of the camera substrate 20. The aperture 50 shuts offdiffusion of light to other directions so as to guide the light emittedfrom the distance-measuring light-emitting devices 52 to the objectdirection.

Separately from the camera substrate 20, a control substrate 60 isprovided. The control substrate 60 is provided for connecting with theoutside, and includes an external connector 62 and a camera connector 64for connecting with the camera substrate 20. The above control substrate60 is disposed on the lower portion of the camera substrate 20, andelectrically connected with the camera substrate 20 using the cameraconnector 64. Further, a holder cover 68 is provided for the externalconnector 62.

In such a way, the image sensor 30, the light-emitting devices 22, 24,the photo-detector devices 26 and the distance-measuring light-emittingdevices 52 are mounted on the camera substrate 20. Also, thepolarization/diffusion plate holders 46, the diffusion plates 44, thepolarizing plates 42, the apertures 50, the optical unit 34, and thelight guide members 10 are mounted on the above camera substrate 20, andthus a camera portion is assembled. To the above camera portion, thecontrol substrate 60 is attached. FIG. 5 shows a state of the unit afterattaching the camera portion and the control substrate 60.

Further, as shown in FIG. 6, there are prepared a visible-light cutofffilter plate 76, a hood 78, a holder assembly 70 and an external case74. By attaching attachment unit shown in FIG. 5 to the holder assembly70 shown in FIG. 6, and also, by attaching the holder cover 68 shown inFIG. 2 to the holder assembly 70, the configuration shown in FIG. 7 isassembled.

The configuration shown in FIG. 7 is then housed into the external case74 shown in FIG. 6, and by attaching the visible-light cutoff filterplate 76 having an attached hood 78 on the upper portion of externalcase 74, an image capturing apparatus shown in FIG. 8 is structured. Theabove the visible-light cutoff filter plate 76 cuts off the visiblelight component so as not to enter the image sensor 30 from outside.Further, as also described in FIG. 1, the hood 78 shuts off the light sothat the light outside the predetermined image capturing area does notenter the optical unit 34, and prevents the light being leaked from thelight guide member 10 from invading into the optical unit 34.

FIG. 1 shows a cross-sectional view of the finished body 1 shown in FIG.8. As described earlier, the image sensor 30, the light-emitting devices22, 24, the photo-detector devices 26 and the distance-measuringlight-emitting device 52 are mounted on the camera substrate 20. Namely,a basic structure including the illumination system and the imagecapturing system is mounted on the single substrate. Accordingly, onlyone mounting board is sufficient, thus contributing to cost reduction.

Also, with the provision of the ring-shaped light guide member 10 on theupper portion of light-emitting devices 22, 24, the light from thelight-emitting devices 22, 24 is guided to the visible-light filter 76.The above light guide member 10 separates the light from thelight-emitting devices 22, 24 and then forwards the light to thevisible-light filter 76. Therefore, the light-emitting devices 22, 24can be disposed close to the image sensor 30, and also on the identicalsubstrate 20, which enables miniaturization, and illumination of theobject by uniform light as well. More specifically, assuming that anoblique line portion of an upside-down triangle shape shown in FIG. 1 isthe image capturing range of the camera, the image capturing range canbe illuminated by uniform light.

Further, because the light guide member 10 has a ring shape, it ispossible to house the optical unit 34 inside the ring 10, thus enablingfurther miniaturization. In addition, the hood 78 prevents the lightoutside the predetermined image capturing range (oblique line portion inFIG. 1) from entering the optical unit 34, and also prevents the lightleaked from the light guide member 10 from invading into the opticalunit 34. Accordingly, even when the light guide member 10 and thelight-emitting devices 22, 24 are disposed close to the image sensor 30and the optical unit 34, degradation in imaging accuracy can be avoided.

Moreover, since the distance-measuring light-emitting devices 52 areprovided on the camera substrate 20, it becomes possible to furtherminiaturize the camera unit measuring the distance. Additionally, inFIG. 1, the control substrate 60 is connected to the lower portion ofthe camera substrate 20, and an external cable 2 is connected to theexternal connector 62 of the control substrate 60.

Illumination Mechanism

Next, an illumination mechanism including a light guide member will bedescribed. FIG. 9 shows an operation explanation diagram of the lightguide member according to one embodiment of the present invention; FIG.10 shows a detailed configuration diagram of the illumination mechanismshown in FIG. 9; FIG. 11 shows an explanation diagram of a trapezoidalnotch of the light guide member shown in FIG. 10; FIGS. 12 through 14show explanation diagrams of light guiding and diffusion operations ofthe light guide member shown in FIG. 10; and FIG. 15 shows a luminance(brightness) distribution diagram by the illumination.

In FIG. 9, like parts as shown in FIGS. 1 and 2 are designated by likereference numerals. As shown in FIG. 9, the light guide member 10 guidesthe light from each light-emitting device 22, 24, which is a point lightsource, to the visible-light filter 76 so as to split the light intothree.

More specifically, from the light guide member 10, basically, light A3to the direction of the optical unit 34, light A2 to the longitudinaldirection of the light guide member 10, and light Al to the oppositedirection to the optical unit 34 are output. With the provision of theabove light guide member 10, each single point light source 22, 24 canbehave as if three point light sources exist in the vicinity of thevisible-light filter 76.

As shown in FIG. 10, the light guide member 10 includes an upper slopeface 14, two side faces 10-1, 10-2, and a lower trapezoidal groove 12.The lower trapezoidal portion 12 is positioned opposite to thelight-emitting device 22, 24 by the intermediary of the polarizing plate42 and the diffusion plate 44, and receives the light from thelight-emitting device 22, 24. Also, the upper slope face 14 is a slopeface of which height is greater on the optical unit 34 side.

As shown in FIG. 11, an emission intensity distribution B from thelight-emitting device 22, 24 has a long (strong) circular arc shape inthe upward direction. Namely, the intensity of a light component B1 tothe light output direction of the light-emitting device 22, 24 (verticaldirection of the device) is stronger than the intensity of lightcomponents B2, B3 to the directions to both sides. As shown in FIG. 9,the trapezoidal groove 12 in the light guide member 10 is formedcorrespondingly to the above intensity distribution B so that the lightcan basically be regarded as three point light sources on the outputside.

More specifically, in order to function as three point light sources bythe reflection inside the light guide member 10, the trapezoidal groove12 is constituted of a flat portion 12 b for introducing the lightcomponent B1 without refracting, and a pair of slope face portions 12 a,12 c for refracting and introducing the light components B2, B3 on theboth sides, having gradients corresponding to the directions of thelight components B2, B3. The above shapes of the trapezoidal groove 12function to virtually split the light from each point light source 22,24 into three.

Also, as described later, the respective lengths of the above flatportion 12 b and slope face portions 12 a, 12 c are set so that thelight intensity in a predetermined area caused by the light output fromthe light guide member 10 becomes substantially uniform. Here, thelength of the flat portion 12 b, which receives the maximum intensity ofthe light component B1, is set shorter than each length of the slopeface portions 12 a, 12 c, which receive light intensity of the lightcomponents B2, B3 weaker than the light intensity of the light componentB1. By this, depending on the light intensity distribution, the splitlight amount is adjusted.

The above operation is described referring to FIGS. 12 through 14. Asshown in FIG. 12, the component B2 on the left side of the emissionintensity distribution B of each light-emitting device 22, 24 isrefracted at the left slope face portion 12 a of the light guide member10, and incident to the left side face 10-2 of the light guide member10. The incident light is then reflected on the left side face 10-2, andforwarded to the right side face 10-1 of the light guide member 10.Subsequently, the light forwarded to the right side face 10-1 isreflected on the right side face 10-1, and forwarded again to the leftside face 10-2. The light is then reflected on the left side face 10-2,and incident to the upper slope face 14 substantially perpendicularly,and output to the outermost portion of the image capturing range.

Also, as shown in FIG. 13, the central component B1 of the emissionintensity distribution B of the light-emitting device 22, 24 is incidentto the light guide member 10 from the central flat portion 12 b of thelight guide member 10. The light is then incident obliquely to the upperslope face 14, and output to the innermost portion of the imagecapturing range.

Further, as shown in FIG. 14, the component B3 on the right side of theemission intensity distribution B of the light-emitting device 22, 24 isrefracted at the right slope face portion 12c of the light guide member10, and incident to the right side face 10-1 of the light guide member10. The incident light is then reflected on the right side face 10-1,and forwarded to the left side face 10-2 of the light guide member 10.Subsequently, the light forwarded to the left side face 10-2 isreflected on the left side face 10-2, and incident to the upper slopeface 14 substantially perpendicularly, and output between the innermostportion and the outermost portion of the image capturing range.

By synthesizing FIGS. 12 through 14, an optical path diagram as shown inFIG. 10 is obtained. Namely, at the trapezoidal groove 12, the lightguide member 10 splits the point emission of the point light source 22,24 into three. Using the reflection on the side faces inside the lightguide member 10, each split light is output in such behavior as threepoint light sources existent on the output side of the light guidemember 10.

In this case, considering the image capturing range (shown by obliquelines) shown in FIG. 1, the output direction is adjusted at the upperslope face 14 of the light guide member 10. Also, in order to obtainsubstantially uniform light intensity in the image capturing range, thelengths i.e. the incident widths of, or the incident amount to, the flatportion 12 b and the slope face portions 12 a, 12 c of the trapezoidalgroove 12 of the light guide member 10 are adjusted, taking intoconsideration the emission intensity distribution B of light-emittingdevice 22, 24 described earlier in FIG. 11.

Here, to obtain the substantially uniform light intensity, because theemission intensity distribution B of the light-emitting device 22, 24described in FIG. 11 has stronger light intensity at the center, whileweaker light intensity in the periphery, the length of the flat portion12 b of the trapezoidal groove 12 is set shorter than each length of theslope face portions 12 a, 12 c. Thus, it is structured that the lightportion having strong light intensity is incident not only to the flatportion 12 b, but also to the slope face portions 12 a, 12 c.

Also, using the groove 12 having a trapezoidal shape and the upper slopeface 14 of the light guide member 10, and the reflection by the lightguide member 10, the reflected light and the rectilinear light can beoutput with diffusion so as to obtain substantially uniform lightintensity throughout the image capturing range.

FIG. 15 shows a diagram illustrating an experiment result in regard tothe image capturing range and the light intensity of the image capturingapparatus shown in FIG. 1. In FIG. 15, the horizontal axis indicates theposition, while the vertical axis indicates the light intensity. Morespecifically, the position is a dot position of the image sensor 30, andhere, the image sensor 30 having 640 dots in width is employed. Byplacing plain white paper for experimental purpose on the flat portionof the upper part of the image capturing range (oblique line portion)shown in FIG. 1, thereby producing uniform reflection, an output levelvalue of each dot of image sensor 30 has been measured. Because of thewhite paper, the output level value corresponds to the light intensity.

According to the above example of the experiment result, substantiallyuniform light intensity has been obtained in the width of approximately310 dots in the center of the image sensor 30. For example, the maximumlevel in the 310 dot width is ‘190’, the minimum level is ‘160’, whichrange within ±15% of the medium value ‘175’, with the error of ±10% orless.

Referring to FIG. 1, for an image capturing range V of the image sensor30, the range of uniform light intensity is shown by V1. Although theimage capturing range is V, by extracting particularly importantfeatures of an imaging object from an image in the range of the aboveV1, highly accurate feature extraction becomes obtainable.

In addition, an image obtained outside the range of V1 may also be usedfor feature extraction of a lower degree of importance, by matching thelevel through level correction.

Image Processing Configuration

FIG. 16 shows a block diagram of a captured image processing apparatusaccording to one embodiment of the present invention. FIG. 17 shows aflow chart of the captured image processing in the above imageprocessing apparatus. Also, FIG. 18 shows an explanation diagram ofdistance measurement operation.

As shown in FIG. 16, a drive/process system in the image capturingapparatus includes a first illumination LED driver 94 for driving thefirst light-emitting device 22, a second illumination LED driver 96 fordriving the second light-emitting device 24, a distance-measuring LEDdriver 98 for driving the distance-measuring light-emitting devices 52,an analog/digital converter 92 for converting the analog output of eachpixel from the image sensor 30 to a digital value, and a microcontroller90.

As described in FIG. 4, the first and second illumination LED drivers94, 96 perform APC (automatic power control) in each light emissionperiod, according to the light intensity received in the photo-detectordevice 26. Microcontroller (MCU) 90 includes MPU (microprocessor), ROM(read-only memory) and RAM (random access memory), and executesprocessing including distance measurement 90A, posture discrimination90B, shutter control 90C and image processing 90D.

Referring to FIG. 17, imaging processing in MCU 90 is described below.

(S10) MCU 90 drives the distance-measuring light-emitting devices (LED)52 via the distance-measuring LED driver 98. By this, fourdistance-measuring light-emitting devices 52 described in FIGS. 2 and 3emit light. As shown in FIG. 1, the image sensor 30 photographs an imagein the image capturing range. Here, since the illuminationlight-emitting devices 22, 24 are not driven, the image sensor 30receives only the reflected light from the object in the image capturingrange corresponding to the light emitted from the distance-measuringlight-emitting devices 52. In FIG. 18, there are shown the positions ofthe reflected light 52A, 52B, 52C and 52D in an image 30A of the imagesensor 30, being received from the object in the image capturing rangecorresponding to the light emitted from each distance-measuringlight-emitting device 52. The above positions deviate depending on theinclination of the object (for example, palm).

(S12) Next, by means of analog/digital (A/D) converter 92, each analoglight reception amount in image 30A of the image sensor 30 is convertedinto a digital value, and then stored into the memory of MCU 90. MCU 90searches the image data in the memory, and detects the positions of theabove reflected light 52A, 52B, 52C and 52D.

At this time, since the four distance-measuring light-emitting devices52 are disposed diagonally from the center of the image (image capturingrange) as shown in FIGS. 3 and 18, by searching on the straight lines,as shown by the dotted lines in FIG. 18, the positions of the fourpoints (i.e. the positions from the center of the image sensor) can bedetected from the pixel luminance on the straight lines. For example, inthe image capturing range of an upside-down triangle as shown in FIG. 1,when the distance to the object is long, the spot light positions on theimage become near the center as shown by 52A1 to 52D1 with the dottedline, while when the distance to the object is short, the spot lightpositions on the image become far from the center as shown by 52A to 52Dwith the solid line.

Further, because the light-emitting devices 52 are disposed in thefarthest positions on the diagonal lines with sufficient distances, itis possible to detect the positions farthest from the center in theimage. From the above four positions, MCU 90 detects the distance(average) and the inclination of the object using the triangulationmeasuring method. Namely, by use of the positions from the center of theimage sensor 30, a distance at each of the four points is calculated,and the inclination (in four directions) can be detected from thedistance difference of the four points.

(S14) MCU 90 decides whether the distance to the imaging object isappropriate (whether the object is positioned in the image capturingrange with a predetermined focal-distance). When the distance to theimaging object is not appropriate, MCU 90 displays a guidance message ona non-illustrated display portion. For example, a guidance message of“Put the object (palm) closer.” or “Put the object (palm) further.” isdisplayed.

(S16) When the distance is appropriate, MCU 90 decides whether theinclination of the imaging object is appropriate. For example, whenimaging a flat portion (palm, etc.) of the object, it is decided whetherthe inclination is within a tolerable range. When the inclination of theimaging object is not appropriate, MCU 90 displays a guidance message onthe non-illustrated display portion. For example, in case that a palm isthe object, a guidance message of “Open your hand.” or the like isdisplayed.

(S18) When the inclination is appropriate, MCU 90 instructs theillumination LED drivers 94, 96 to emit light. Thus, the first andsecond light-emitting devices 22, 24 emit light, so as to irradiate theobject. Subsequently, MCU 90 drives a non-illustrated electric shutter(provided in the optical unit), and photographs the image in the imagecapturing range by image sensor 30. MCU 90 then stores the image intothe memory via A/D converter 92. Then, the feature is extracted from theabove image. For example, in case of extraction of the aforementionedblood vessel image, the blood vessel image is extracted from the image.

As such, the image sensor 30 is also used for the distance-measuringphotodetector portion to detect whether the imaging object lies at thefocal distance, or the inclination thereof. Thus, in the distancemeasurement mechanism, it is sufficient to provide thedistance-measuring light-emitting devices 52 without particularlyproviding photodetector devices for distance measurement. Thiscontributes a reduction of cost, and miniaturization as well, due to areduced number of mounting components.

Also, because four distance-measuring light-emitting devices 52 aredisposed diagonally from the center of the image (imaging range), thepositions of the four points can be detected by searching the image datastored in the memory as shown by the dotted lines in FIG. 18, and thus,detection processing becomes easy. Further, because thedistance-measuring light-emitting devices 52 are disposed in thefarthest positions on the diagonal lines with sufficient distances, itis possible to detect the farthest positions in the image from thecenter even the apparatus is miniaturized, and detection of theinclination can be performed accurately.

Other Embodiments

In the aforementioned embodiment, the description is made using a caseof four distance-measuring light-emitting devices. However, to detectthe inclination, it is sufficient if three devices are provided at theminimum. Similarly, when it is not necessary to detect inclination, onlyone distance-measuring light-emitting device may be provided.

Also, in the aforementioned embodiment, the description is made usingthe lower groove 12 of a trapezoidal shape. However, other polyhedronshapes are applicable. For example, in the above description, the groovehas three planes because of the trapezoidal cross section, but a grooveof a polyhedron shape such as having four planes may be used dependingon required performance. When attaching importance to the cost, apolyhedron having a smaller number of faces is better, and therefore, atrapezoid is better here.

In the aforementioned embodiments, the imaging object is exemplified bythe palm, and the image processing of the imaging object is exemplifiedby the vein pattern authentication. However, the present invention isalso applicable to other biometric authentication by use of otherfeatures of human bodies, including hand skin pattern, blood vesselimage of the back of hand, blood vessel image of a finger, and featuresof face and iris, etc. Also, the present invention is not limited to theapplication to the biometric authentication, but applicable to otherapplications.

While the embodiments of the present invention have been illustrated inthe foregoing description, any suitable modifications can be madewithout departing from the spirit of the invention. All suchmodifications are not to be excluded from the scope of the invention.The features and advantages of the invention which fall within the scopeof the invention are covered by the appended claims.

1. An image capturing apparatus for capturing an image of an object byilluminating the object and receiving reflected light from the object,comprising: an image sensor for capturing the image by receiving thereflected light; an illumination mechanism for illuminating the objectat the time of image capturing and disposed in the periphery of theimage sensor: at least three distance-measuring light-emitting devicesfor irradiating the object with spot light and disposed on differentpositions of an outer position of the illumination mechanism; and acontrol circuit for driving the distance-measuring light-emittingdevices, detecting the spot light positions of the distance-measuringlight-emitting devices from the image captured by the image sensor, andobtaining a distance to the object and an inclination of the object fromthe detected positions, judging whether or not the object positions andthe inclination are within an image capturing range, and driving theillumination mechanism to capture the image of the object by the imagesensor.
 2. The image capturing apparatus according to claim 1, whereinthe at least three distance-measuring light-emitting devices aredisposed in opposite positions centered at the image sensor.
 3. Theimage capturing apparatus according to claim 1, wherein thedistance-measuring light-emitting devices are mounted on a circuit boardhaving the image sensor mounted thereon.
 4. The image capturingapparatus according to claim 1, wherein the image sensor captures animage of a portion of a living body.
 5. The image capturing apparatusaccording to claim 1, wherein the illumination mechanism comprises: aplurality of light-emitting devices mounted in the peripheral positionsof the image sensor; and a ring-shaped light guide member for guidingthe light of the plurality of light-emitting devices to an imagecapturing range and illuminating the image capturing range, and whereinfurther comprises an optical unit accommodated inside the ring of thering-shaped light guide member and for guiding reflected light of theobject in the illuminated image capturing range to the image sensor. 6.The image capturing apparatus according to claim 5, further comprising adiffusion plate for diffusing the light of the light-emitting devicesand disposed between the ring-shaped light guide member and theplurality of light-emitting devices.
 7. The image capturing apparatusaccording to claim 5, wherein the plurality of light-emitting devicesare configured of light-emitting devices for emitting infrared rays, andwherein at least on the incident plane of the optical unit, an opticalfilter for filtering the visible light is disposed.
 8. The imagecapturing apparatus according to claim 5, wherein the light guide membercomprises: a lower end portion for guiding the light of thelight-emitting devices; an upper end portion for outputting the light inthe image capturing range; and a light guide portion for guiding thelight of the light-emitting devices from the lower end portion to theupper end portion.
 9. The image capturing apparatus according to claim5, further comprising a circuit board mounted with the image sensor, thedistance-measuring light-emitting devices and the plurality oflight-emitting devices.
 10. The image capturing apparatus according toclaim 9, wherein the plurality of light-emitting devices are mounted onthe circuit board at predetermined intervals along a circle in theperiphery of the image sensor, and wherein the light guide member has aring-shaped structure corresponding to the circle.